Brake cylinder maintaining valve

ABSTRACT

A brake cylinder maintaining valve may include spool valves or poppet valves. When the pressure in the brake cylinder drops below its original set pressure, such a maintaining valve may feed brake pipe (BP) pressure through a choke to replenish and maintain brake cylinder (BC) pressure up to a certain point. If the leak is too great, such as when it exceeds the capacity of the choke, the brake cylinder pressure will not be maintained. Such a maintaining valve may be either integrated into the control valve, or it may be mounted remotely to the brake system. If mounted remotely, it may be connected by multiple ways, including through a conventional 4-port access plate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims the prioritybenefit of copending U.S. patent application Ser. No. 13/652,896, filedon Oct. 16, 2012, the entire contents of which are incorporated hereinby reference.

BACKGROUND AND SUMMARY

The present disclosure relates generally to control valves for use infreight car brake equipment, and more particularly to a valve thatmaintains the brake cylinder pressure in such control valves.

Control valves used in freight car brake equipment (e.g., the DB-60control valve manufactured by New York Air Brake Corporation, Watertown,N.Y. USA or the ABDX control valve manufactured by Wabtec Corporation,Wilmerding, Pa. USA) are well known. If such control valves supply airpressure to the brake cylinder of a freight car, and the plumbingbetween the control valve and the freight car has a leak, then the brakecylinder will not maintain the original set pressure. This could be dueto, for example, a leaking packing cup in the brake cylinder, a leakinghose, or any other reason that would lead to the leaking of pressurebetween the connection of the control valve and the brake cylinder.

One means of avoiding such problems may be to have a valve thatmaintains the brake cylinder pressure. When the pressure in the brakecylinder drops below its original set pressure, such a maintaining valvemay feed brake pipe (BP) pressure through a choke to replenish andmaintain brake cylinder (BC) pressure up to a certain point. If the leakis too great (i.e., to the extent it exceeds the capacity of the choke),the brake cylinder will not be maintained. Such a maintaining valve maybe either integrated into the control valve, or it may be mountedremotely to the brake system. If mounted remotely, it may be connectedby multiple ways, including through a conventional 4-port access plate.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of freight car brake equipment according to theprior art;

FIG. 2 is a diagrammatic view of a service portion of a brake controlvalve used in the freight car brake equipment shown in FIG. 1;

FIG. 3 is a diagrammatic view of a brake cylinder maintaining valveaccording to one embodiment of the present invention;

FIG. 4 is a diagrammatic view of a brake cylinder maintaining valveaccording to another embodiment of the present invention;

FIG. 5 is a diagrammatic view of a brake cylinder maintaining valve inits charging lap position utilizing a sandwich plate between the serviceportion of the brake control valve and its release valve;

FIG. 6 is a diagrammatic view of a brake cylinder maintaining valve inits service lap position utilizing a sandwich plate between the serviceportion of the brake control valve and its release valve;

FIG. 7 is a diagrammatic view of an ABDX-type brake cylinder maintainingvalve in its charging lap position; and

FIG. 8 is a diagrammatic view of an ABDX-type brake cylinder maintainingvalve in its service lap position.

FIG. 9 is a diagrammatic view of a brake cylinder maintaining valveintegrated into the control valve in its charging lap position;

FIG. 10 is a diagrammatic view of a brake cylinder maintaining valveintegrated into the control valve in its service lap position;

FIG. 11 is a diagrammatic view of a brake cylinder maintaining valveshown as a sandwich plate between the service portion and release valveand in its service lap position; and

FIG. 12 is a brake cylinder maintaining valve according to still anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments are discussed in detail below. While specificexemplary embodiments are discussed, it should be understood that thisis done for illustration purposes only. In describing and illustratingthe exemplary embodiments, specific terminology is employed for the sakeof clarity. However, the embodiments are not intended to be limited tothe specific terminology so selected. Persons of ordinary skill in therelevant art will recognize that other components and configurations maybe used without departing from the true spirit and scope of theembodiments. It is to be understood that each specific element includesall technical equivalents that operate in a similar manner to accomplisha similar purpose. The examples and embodiments described herein arenon-limiting examples.

Referring now to the drawings, wherein like reference numerals andcharacters represent like or corresponding parts and steps throughouteach of the views, there is shown in FIG. 1 a schematic representationof a brake system associated with a prior art freight or rail car 100.The system may be used to operate air brakes (not shown) in accordancewith known embodiments of the prior art. As illustrated, the freight carbrake equipment includes a brake control valve 102 having a serviceportion 104 and an emergency portion 106 connected to a pipe bracket108. A cut-off cock 110 connects, through a branch pipe tee 112, brakepipe 114 to the pipe bracket 108 at port BP. A retaining valve 116connected to exhaust is connected to pipe bracket 108 at retainer portRET. A combined reservoir 118, having an auxiliary AUX RES and anemergency reservoir EMER RES is connected to respective ports AR and ERof pipe bracket 108. A brake cylinder 120 may be connected through anempty/load device (not shown) to brake cylinder port BC. The elementsdescribed so far are part of normal freight car brake equipment. Theservice portion 104, emergency portion 106, and pipe bracket 108 arestandard parts, for example, a DB-60 from New York Air Brake Corporationor Knorr Bremse AG. Similarly, they may be an ABDX or other AAR approvedbrake valves.

Air used to operate the brakes on rail cars may be transmitted throughbrake pipe 114 to brake control valve 102, and may accumulate incombined reservoir 118. Brake pipe 114 may be coupled with correspondingbrake pipes in attached rail cars (not shown) through AAR standard airbrake hoses 122 to form a train line operable to communicate air from anassociated locomotive (not shown) to each rail car 100 attached to thelocomotive as part of a train. Brake pipe 114 may serve at least twopurposes. First, air may travel through brake pipe 114 to accumulate incombined reservoir 118 for each individual rail car 100. Second, brakepipe 114 may facilitate transmission of a pressure drop that activatesrespective brakes associated with each rail car 100.

Although the improvement herein will be shown in FIGS. 3-10 to have beenincorporated into the service portion of the DB-60, the presentimprovement may be provided to any brake control valve portion whichincludes a piston responsive to brake pipe pressure on one side and areservoir as the source of brake cylinder pressure on the other side ofthe diaphragm. Thus, the invention may be used in other AAR-styled brakecontrol valves or non-AAR brake control valves, including ABDX-typecontrol valves as shown in FIGS. 7-8. Only those portions of the serviceportion of the DB-60 and ADBX which explain the operation of the presentinvention have been included in the schematics and others have beenintentionally deleted for sake of clarity.

Pipe bracket 108 supports and aligns both service 104 and emergency 106portions and supplies air to the valvular components. The precontrolledflow of air to and from the brake pipe 114, brake cylinder 120, combinedauxiliary/emergency reservoir 118 and retaining valve 116 is alsodirected through the pipe bracket 108 to which all connections are made,with butt or socket welded flange fittings.

The specific functions of the service portion 104 are to supply air tothe combined reservoir 116 during initial charging of the system andrecharging following release of an application; to direct auxiliaryreservoir AR air into the brake cylinder 118 depending on apredetermined rate and amount of brake pipe pressure reduction; toexhaust brake cylinder BC air during release after an application; toguarantee stability of the brake system in release condition againstundesired application of the brakes which may result from permissiblebrake system leakage; and to guarantee stability of the brake system inservice lap condition against undesired release of the brakes which mayresult from permissible auxiliary reservoir leakage. The service portion104 also functions to support recharge of the brake system during therelease of a service application by feeding emergency reservoir ER airinto the brake pipe 112 independent from the main piston system; toguarantee minimum reduction during initial brake pipe reduction andmaintain minimum brake cylinder BC pressure by connecting quick servicechamber QS-Ch. and brake cylinder BC pressures; to support initial brakepipe reduction by venting brake pipe BP air to the atmosphere ATM duringthe preliminary quick service stage; to support recharge of the brakesystem after manual release subsequent to an emergency application byconnecting the pressure of the auxiliary reservoir to the brake pipe112, to permit exhaust of retainer held brake cylinder pressure in theretainer pipe and volumes during manual release subsequent to a servicereduction; to directly release brake cylinder pressure independent ofthe main piston system after any application by manual activation of therelease handle; to provide manual drain means for auxiliary reservoirand emergency reservoir pressures; and to release the main piston systemafter a service application by manual activation of release handle.

In order to perform these functions, the service portion 104 is equippedwith the following subcomponents.

As shown in FIG. 2, the service main piston 202 compares brake pipe BPand auxiliary reservoir AR pressures acting on equal areas. Auxiliaryreservoir charging 204, emergency reservoir charging 206, and balancingvalves 208 are spaced uniformly at 120° intervals around the samediameter and are mechanically operated by the bottom side of the piston.The coaxially arranged balancing piston 210 is pressurized withauxiliary reservoir AR air by the balancing valve 208 and acts on thebalancing spring 212 which stabilizes the main piston system 202 inservice lap position.

The main piston 202 operates the quick service inlet valve 214, whichallows brake pipe BP air to flow to the quick service chamber (QS-Ch.).The auxiliary reservoir/brake cylinder inlet 216 and brakecylinder/retainer outlet valves 218 are also mechanically operated bythe main piston 202. Stability of the main piston system 202 in therelease position is provided by means of the sensitivity 220 andstability chokes 222; stability in the service lap positions is providedby means of the stability choke 222. A separate emergency reservoircharging check valve/choke 224 arrangement prevents uncontrolled returnflow of emergency reservoir ER air into the auxiliary reservoir whenreleasing the brakes from a service application. Thus, no undesiredreapplication of the brakes will occur during release.

A metal reinforced rubber diaphragm 225 of the service acceleratedrelease valve 226 also compares brake pipe BP and auxiliary reservoir ARpressures acting on equal areas; this component operates independentlyof the service main piston system 202. When the service acceleratedrelease valve 226 is triggered, emergency reservoir ER air passes by thehigh sensitivity back flow check valve 228 into the brake pipe BP.

A metal reinforced rubber diaphragm 231 of the quick service limitingvalve 230 is pressurized by brake cylinder BC air and allows restrictedflow of brake pipe/quick service air to the brake cylinder 118 to apredetermined value. The quick service limiting check valve 232 preventsreturn flow of brake cylinder BC air to atmosphere ATM during emergencyapplications and in the event of a retainer is being set in “highpressure retaining” position with the service main piston system 202 inthe release position.

A metal reinforced rubber diaphragm 233 of the emergency releaseauxiliary reservoir reduction valve 234 is pressurized by brake pipe andbrake cylinder air in opposite sides. After manual release of brakecylinder pressure subsequent to an emergency application, increasingbrake pipe pressure during recharging operates the valve and allowsauxiliary reservoir air to flow via the emergency release auxiliaryreservoir reduction check valve 234 into the brake pipe and assistsduring brake pipe recharging. The retaining check valve 236, by means ofa choke, allows reduction of retainer held brake cylinder air to apressure level which allows the brake cylinder piston to move to releaseposition.

The quick service valve 238 piston is pressurized by auxiliary reservoirAR air on one side and controls the flow of quick service QS air toatmosphere ATM. As soon as the service main piston system 202 allows thebalancing valve 208 to pressurize the larger opposite area of the quickservice valve piston with auxiliary reservoir air, the venting of quickservice/brake pipe air will be interrupted. The piston of release valve240 is pressurized on both sides with brake cylinder BC air and sealsthe connection from brake cylinder 120 to atmosphere ATM.

Upon activation of the release valve handle 242, the upper side of thepiston is vented through the release exhaust valve 244 which allows thepiston to open the passage from brake cylinder 120 to atmosphere ATM.The piston remains in this position until brake cylinder lockup pressurebelow the piston is released by the service main piston system 202 uponits release. Auxiliary reservoir exhaust 246 and emergency reservoirexhaust 248 valves are mechanically operated by the release valve lifter250 and allow high capacity flow of auxiliary reservoir/emergencyreservoir air to the atmosphere in order to drain the brake system.

Charging Lap Position

Compressed air from the brake pipe 114 flows into the pipe bracket 108via the combined dirt collector and cut-out cock. One flow path leadsthrough the pipe bracket strainer into the service 104 and emergency 106portions to supply those with filtered air. The other flow path bypassesthe pipe bracket strainer and leads to the vent valve (not shown) in theemergency portion 106 to allow unrestricted venting of brake pipe BP airduring an emergency application. During charging, brake pipe airpressurizes the following valve components:

Brake pipe BP air pressurizes the main piston, the valve seat area 214,and flows to the service accelerated release valve 226 and the emergencyrelease auxiliary reservoir reduction valve 234. The auxiliary reservoiris charged directly by the service main piston system 202. From thebrake pipe 118, the air flows via choke 220 and an open valve seat 204to the volume below the main piston, pressurizing the upper side ofbalancing piston 210. Auxiliary reservoir air further flows to the AR/BCinlet valve 216, to the release valve 240, to the valve seat in thebalancing valve 208, to the quick service valve 238 and the auxiliaryreservoir via the pipe bracket 108. Additional auxiliary reservoircharging is accomplished by air flow via stability choke 222.

If, during charging, the pressure differential created by chokes 220 and222 across the main piston exceeds a predetermined value, the mainpiston moves into retarded recharge position and returns to charging lapposition when brake pipe BP and auxiliary reservoir AR pressuresapproach equalization.

The emergency reservoir is charged from auxiliary reservoir air via openvalve seat 206. The auxiliary reservoir AR air in the volume below themain piston 202 flows via an open valve seat in the emergency reservoircharging check valve 224 to the service accelerated release valve 226,to the release valve 240, to the emergency portion (not shown) and viathe pipe bracket 118 into the emergency reservoir.

The left side of diaphragm 225 is pressurized with brake pipe BP air,the right side with auxiliary reservoir AR air. Emergency reservoir ERair flows to the closed valve seat via back flow check valve 228. Theleft side of diaphragm 233 is pressurized with brake pipe BP air. Thediaphragm 233 is thereby forced on its right-hand stop against the forceof a spring. Simultaneously, the emergency release auxiliary reservoirreduction check valve 239 is forced on its valve seat by the combinedforces of a spring and brake pipe BP pressure.

Auxiliary reservoir AR air in the volume below the main piston alsopressurizes the upper area of piston 241. The piston 241 is therebyforced downward and opens the valve seat against the force of thespring. Auxiliary reservoir AR air pressurizes auxiliary reservoirexhaust valve 246. Emergency reservoir ER air pressurizes emergencyreservoir exhaust valve 248.

Service Lap Position

During a service brake application, the brake cylinder is charged fromthe auxiliary reservoir by the service main piston system 202. As soonas the auxiliary reservoir pressure is reduced to approximately thevalue of the brake pipe pressure, the service main piston system 202moves from the service position to the service lap position. Herewith,valve seat 216 is closed and the flow path between auxiliary reservoirand brake cylinder is interrupted. The balancing piston 210 acts on thebalancing spring 212 through its spring guide. This introduces a definedforce in the service main piston system 202, which holds it in theservice lap position.

Brake pipe BP and auxiliary reservoir AR are connected through the verysmall stability choke 222 which determines the release stability. Duringa further brake pipe reduction, the service main piston system 202 willagain move the service position, and the flow path from auxiliaryreservoir to brake cylinder will be opened. Subsequently, the sameprocedure as described above will take place and move the service mainpiston system 202 back again to service lap position. The reduction ofbrake pipe pressure and hence the increase in brake cylinder pressurecan be continued until the auxiliary reservoir pressure is equal to thebrake cylinder pressure. A further reduction of brake pipe pressure doesnot affect the level of the brake cylinder pressure during a serviceapplication, but moves the main piston system 202 to the serviceposition. The quick service limiting valve 230 assures a predeterminedminimum brake cylinder pressure. Should the brake cylinder pressure dropbelow this value—for example, due to brake cylinder leakage—the quickservice limiting valve 230 will open and feed brake pipe pressure viathe quick service chamber to brake cylinder.

In the service lap position, the control valve has moved from charginglap and undertaken the following steps. The first step is quick service,where BP is reduced lower than AR to the point that the quick servicecheck valve 214 is opened and the valve moves up into the service zone.Once the valve is in the service zone, the valve fills AR pressure intoBC through check 216. The valve continues to fill BC until BP and AR areroughly equal. The limiting valve 230 will run until BC pressure underdiaphragm 231 reaches about 8 to 12 pounds per square inch. At thispoint, the quick service limiting valve 230 will shut off Once the ARand BP are roughly equalized and the filling of BC has been completed,the valve is in service lap.

Referring now to FIG. 3, there is shown a brake cylinder (BC)maintaining valve 300 according to a first embodiment of the presentinvention. This poppet valve embodiment is shown in the service lapposition. Accordingly, the valve 300 has made a brake application wherethe valve has charged BC up to its set point. At this point, BC1 isroughly 15 psi lower than BC2. If BC starts to leak, then BC2 pressurewill become lower than BC1 and the diaphragm 302 will move down openingcheck valve 304, allowing BP air to flow into BC which will do so untilBC pressure is maintained to roughly the original set pressure. Duringthe release of the valves, there will be a rise in BP pressure, and whenBP becomes greater than AR diaphragm 306 will open check valve 308 andexhaust the trapped air putting the valve back into charging lapposition.

The spool design shown in FIG. 4 has the same function as the poppetdesign shown in FIG. 3, but it has been designed using spool valvetechnology. This valve 400 is in the state where the control valve hasgone into the service lap position where BC2 is roughly 15 psi lowerthan BC1. If BC starts to leak, then BC1 pressure will become lower thanBC2, and the spool valve 402 will move down connecting BP to BC. Thiswill stay connected until BC has been maintained to roughly the originalset pressure. During the release of the valve, there will be a rise inBP, and when BP becomes greater than AR, spool valve 404 will move upconnecting the trapped BC to atmosphere. This will put the BCmaintaining valve 400 back to its initial charging state.

Referring now to FIGS. 5 and 6, the operation of the brake cylindermaintaining valve utilizing a sandwich plate between the service portionof the brake control valve and its release valve will now be described.During charging or release, valve 505 will be open to atmosphere whichwill exhaust the reference BC pressure on top of diaphragm 502. In thecharging lap position (i.e., where BP is about equal to AR) as shown inFIG. 5, exhaust check valve 505 will be open. Once in a serviceapplication, BC pressure under diaphragm 502 is substantially equal tothe actual brake cylinder (BC) pressure. On top of diaphragm 502, BC isroughly 15 psi lower than the pressure in the brake cylinder (BC). This15 psi difference is created by the cracking pressure of check valve503.

If a leakage occurs, the BC pressure under diaphragm 502 will becomelower than the pressure on top of the diaphragm 502 causing thediaphragm 502 to open check valve 504 and maintain BC against theleakage in the brake cylinder by supplying BP air through valve 504. Itshould also be noted that check valve 503 could be removed and checkvalve 505 could be ported to BC and used as the feed check valve for thereference BC air. In such a manner, when the reference air is exhaustedit will be exhausted to the retainer line RET. The brake cylindermaintaining valve may be integrated (see, e.g., FIGS. 9 and 10) into thecontrol valves of either a DB-60 or an ABDX and on either side, eitherin the emergency portion or in the service portion. It may be preferableif it is on the service portion side, where it can be upstream of therelease valve so the lock out feature of the release valve will work.

For example, FIGS. 7 and 8 illustrate its incorporation into anABDX-type control valve 700. In charging lap, port 701 vents BC air fromthe top of diaphragm 703. Also, port 708 will not be connected to supplythe quick service limiting valve 705. So when the valve 700 is in thisposition there will be no BC maintaining. In service lap (as shown inFIG. 8), the control valve 700 has moved from charging lap and gonethrough the following steps.

The first step is quick service where BP is reduced lower than AR to thepoint that the quick service is opened and the valve moves up into theservice zone. Once the valve is in the service zone, the valve fills ARpressure into BC. The valve continues to fill BC until BP and AR areroughly equal. The limiting valve will run until BC pressure underdiaphragm 703 reaches 8 to 12 psi.

At this point, the quick service limiting valve 705 will shut off.During this time, BC pressure will open the back flow check valve 706which has a high enough cracking pressure to not to interfere with thefunction of the limiting valve. Once the AR and BP are roughly equalizedand the filling of BC has been completed the valve is in service lap.

Once in service lap, if the BC leaks off then the BC pressure under thediaphragm 703 will become lower than the original reference pressurewhich is bottled on top of the diaphragm due to port 701 being closedwhen the valve is in the service zone. Once the pressure differential ishigh enough, the diaphragm will push the spool down opening port 704allowing BP to flow into BC until diaphragm 703 is balanced again. Oncethe valve moves back to its charging lap position, port 701 opens andthe bottled air is released putting the modified limiting valve 705 backinto charging lap position. And, the BC pressure is exhausted toatmosphere.

FIGS. 9 and 10 are diagrammatic views of a brake cylinder maintainingvalve integrated into the control valve in its charging lap and servicelap positions, respectively. In the charging lap position as shown inFIG. 9, check 901 will be venting BC air from the top of diaphragm 905.Also, there will be no air in the quick service chamber QS Ch. to supplythe modified limiting valve 230′. So when the valve is in this positionthere will be no BC maintaining.

In its service lap position as shown in FIG. 10, the control valve hasmoved from charging lap and gone through the following steps. The firststep is quick service, where BP is reduced lower than AR to the pointthat the quick service check 909 is opened and the valve moves up intothe service zone. Once the valve is in the service zone, the valve fillsAR pressure into BC through check 910, and the valve continues to fillBC until BP and AR are roughly equal. The quick service limiting valve230′ will run until BC pressure under diaphragm 905 reaches 8 to 12 psi.At this point, the quick service limiting valve 230′ will shut off.During this time, BC pressure will open the back flow check 904, whichhas a high enough cracking pressure to not interfere with the functionof the quick service limiting valve 230′. Once the AR and BP are roughlyequalized and the filling of BC has been completed, the valve is inservice lap. Once in service lap, if the BC leaks off, then the BCpressure under the diaphragm 905 will become lower than the originalreference pressure, which is bottled on top of the diaphragm 905 due tocheck 901 being closed when the valve is in the service zone. Once thepressure differential is high enough, the diaphragm will push the check906 open allowing BP to flow into BC until diaphragm 905 is balancedagain.

Once the valve moves back to its charging lap position, check 901 isopened and the bottled air is released putting the modified quickservice limiting valve 230′ back into charging lap position. And the BCpressure is exhausted to atmosphere.

FIG. 11 shows yet another embodiment of a brake cylinder maintainingvalve 1100. According to this embodiment (which is shown in its servicelap position), the valve 1100 is in its home position. During a serviceapplication, BC pressure will enter volume 1103 through check 1102 whichwill have a cracking pressure of roughly 15 psi. Once in service lap, ifBC leaks, the pressure on top of diaphragm 1104 will be greater than thepressure under the diaphragm causing the diaphragm to open check 1105.This, in turn, will supply BP pressure to the brake cylinder tocompensate for the leak therein. Check 1106 will then keep BC fromflowing back into BP in the event that BP is lower than BC this could beduring an over reduction or during an emergency application. During therelease of the valve 1100, BP will be greater than AR, which will causediaphragm 1101 to move down and open check 1102. This, in turn, willallow the bottled BC air to exhaust out through the retainer line.

FIG. 12 shows still another embodiment of a brake cylinder maintainingvalve 1200. In contrast to the embodiment shown in FIGS. 9 and 10 (wherethe reference pressure is charged through back flow check 904 from BC1),the embodiment shown in FIG. 12 charges from the same back flow check904 but from BC2. In regards to exhausting in the embodiment shown inFIGS. 9 and 10, such exhausting takes place through check 901. Theexhausting takes place in the embodiment shown in FIG. 12 through anexhaust valve 1202 into BC1.

Although the present brake cylinder maintaining valve has been describedand illustrated in detail, it is to be clearly understood that the sameis by way of illustration and example only, and is not to be taken byway of limitation. The scope of the present invention is to be limitedonly by the terms of the appended claims.

What is claimed:
 1. A brake cylinder maintaining valve for maintainingbrake cylinder pressure in freight car brake equipment, comprising: afirst valve including a diaphragm with a brake pipe pressure on an uppersurface thereof and an auxiliary reservoir pressure on a lower surfacethereof; a first check valve coupled to said first valve and havingauxiliary reserve and atmospheric pressures on opposing surfacesthereof; a second valve including a diaphragm with a first brakecylinder pressure on an upper surface thereof and a second brakecylinder pressure on a lower surface thereof; a second check valvecoupled to said second valve and having the second brake cylinderpressure and the brake pipe pressure on opposing surfaces thereof; andwherein the second check valve provides the brake pipe pressure througha choke to replenish the second brake cylinder pressure if the secondbrake cylinder pressure is below an original set pressure represented bythe first brake cylinder pressure.
 2. The brake cylinder maintainingvalve according to claim 1, wherein in a service lap position the firstbrake cylinder pressure is substantially equal to the second brakecylinder pressure.
 3. The brake cylinder maintaining valve according toclaim 2, wherein said diaphragm of said second valve is adapted to movewhen the first brake cylinder pressure is less than the second brakecylinder pressure by a predetermined amount, thereby opening said firstcheck valve and allowing the brake pipe pressure to replenish the secondbrake cylinder pressure to said original set pressure.
 4. The brakecylinder maintaining valve according to claim 3, wherein saidpredetermined amount comprises about 8 to 12 pounds per square inch(PSI).
 5. The brake cylinder maintaining valve according to claim 4,wherein said predetermined amount comprises about 8 pounds per squareinch (PSI).
 6. The brake cylinder maintaining valve according to claim1, wherein said original set pressure is charged from the second brakepipe pressure.
 7. The brake cylinder maintaining valve according toclaim 1, wherein said original set pressure is charged through a supplyvalve.
 8. The brake cylinder maintaining valve according to claim 1,wherein said original set pressure is exhausted through an exhaustvalve.
 9. The brake cylinder maintaining valve according to claim 1,wherein said diaphragm of said first valve is adapted to move when thebrake pipe pressure is greater than the auxiliary reserve pressure,thereby opening said first check valve, exhausting the first brakecylinder pressure to atmosphere, and returning the brake cylindermaintaining valve to its charging lap position.